The present invention relates to the manufacturing of structural components. More specifically, the present invention relates to the manufacturing of structural components utilized in the automotive industry by exploiting the advantages of roll bonding and/or hydroforming.
As is well known, roll bonding is an efficient method of creating certain metal components. In this process, two sheets of material are introduced to a roll bonding mill whereby they are compressed or sandwiched together to create a molecular bond between the two sheets. By selectively patterning a bond inhibitor (e.g. a graphite, titanium dioxide (TiO2), or like material) the bond can be created in selected areas while avoided in other areas. The two sheets of material can be selectively separated at a later time (as dictated by the bond pattern), to create several structural components. For example, manifolds that require fluid flow in a predetermined pattern or area can easily be fabricated utilizing this process. The process of roll bonding is further outlined in U.S. Pat. Nos. 3,340,589 and 2,957,230.
As appreciated by those familiar with this technology, roll bonding is best suited for relatively thin sheets of material. Using these thinner sheets allows for the easy handling by the rolling mill because only limited separation between work rolls is required. Consequently, roll bonding has traditionally been best suited for non-structural components such as manifolds, etc.
In automotive applications, there are needs for all types of manufactured components. One such category is structural components such as frames, load bearing members, bracketry, etc. Naturally, many of these have a fairly significant weight handling and strength requirements. Consequently, when trying to implement these structural components in aluminum, structural aluminum is typically best suited. This structural aluminum includes 5,000 and 6,000 series aluminum alloys which typically contain some portion of magnesium. 3,000 series alloys may also be used.
Due to the magnesium contained in typical structural aluminum, it traditionally has not been easily roll bonded. When heated prior to introduction into the roll bonding press, an oxide is often created on the surface. This oxide prohibits the aluminum from easily being bonded. The weight handling requirements, combined with the complications of roll bonding structural aluminum, have typically suggested that roll bonded structures could not be easily used for these automotive applications.
In addition to the weight handling capabilities that are required for automotive component applications, actual weight is a continuing consideration. Naturally, automakers are constantly looking for ways to reduce weight, thus increasing fuel economy, etc. This naturally suggests that aluminum would be an appropriate material for use in automotive components due to its weight characteristics. However, aluminum has inherent strength constraints. Consequently, steel has traditionally been used to achieve the required strength and other methods have been attempted to reduce weight.
As mentioned above, certain structural aluminum alloys certainly do display strength characteristics which would allow their use as structural components. Two primary complications exist with the use of aluminum components, however: (1) the aforementioned complications in roll bonding high strength aluminum alloys, and (2) additional raw material required to achieve the necessary strengths. To obtain these necessary strengths, heavier gauges of material is often required. This inherently requires the use of more raw materialsxe2x80x94a raw material which is more expensive than steel to start with. Consequently, other methods (beyond simply using heavier gauge materials) are necessary in order to achieve the desired strength while staying within cost constraints.
Roll bonding itself provides further advantages by allowing the formation of complex structures due to the ability to create intricate patterns of bond inhibitor. More specifically, curves and/or bends can easily be created by appropriate patterning of the bond inhibiting material pattern. Similarly, diameter variations can also be easily accomplished.
In light of the above advantages, it would be beneficial to utilize the processes of roll bonding to create structural members.
A technology which is becoming widely used in the fabrication of structural components is hydroforming. As is well known, hydroforming involves the placement of a preformed blank within the hydroforming die and injecting a fluid into a closed interior cavity of the blank. The fluid is pressurized to a predetermined level, which causes the blank to expand until meeting the interior wall surface of the die. Hydroforming is a very advantageous process in that various configurations can be easily achieved. Most hydroforming processes utilize a traditional blank which is configured as a typical tube of some type. This tube may be a blank pipe, or make take on other shapes. In order to accomplish forming, the blank must include an enclosed cavity to accommodate fluid injection.
Traditionally, hydroforming of complex structures is not possible due to various limitations in tube forming and product expansion. As it is well known, products cannot be expanded beyond certain limits. Further, hydroforming of flat blanks (or blank structures which are substantially flat when placed in the hydroforming die) is very complex and traditionally impractical. As previously mentioned, the base material cannot realistically be expanded beyond a certain level. Consequently, the aforementioned tubes have been used as a convenient starting point because only limited expansion has been required.
As can be appreciated, roll bonding further provides advantages in the formation of complex structures due to the ability to create very intricate patterns. More specifically, curves and/or bends can easily be created by appropriate forming of the bond inhibiting material pattern. Similarly, diameter variations can also be easily accomplished.
In light of the above advantages, it would also be beneficial to combine the processes of roll bonding and hydroforming to create structural members.
In order to capitalize on all the manufacturing efficiencies typically involved with roll bonding and hydroforming, the present invention incorporates various aspects of both processes to create structural components. While both hydroforming and roll bonding is described below, clearly various aspects of either process alone could advantageously be utilized to create structural components.
To begin the process, roll bonding of structural aluminum is done utilizing a modified process. As previously mentioned, roll bonding of structural aluminum has traditionally not been practical due to the formation of oxides on the surfaces of these aluminum alloys. In order to avoid the creation of oxides, the structural aluminum component is manufactured by a lower temperature, quick preheating step which eliminates the creation of oxides on the surfaces while performing the necessary material preparation. As an additional measure, the preheating chamber could easily be treated with nitrogen as further step in avoiding oxide formation. In order to create the required configuration of parts, the bond inhibitor, or xe2x80x9cstop weldxe2x80x9d can be appropriately patterned on the raw material. This is then sent through the roll bonding mill. The roll bonded stock is then stamped in predetermined patterns which correspond to the roll bonding pattern, to create flat stock blanks.
These flat stock blanks are then hydroformed into structural members. A unique hydroforming process is used which includes some preforming, in order to accommodate insertion into the hydroformed structure. Also, a hydroform tool is required for controlling the expansion of the aluminum during the hydroformed process.
The hydroform process itself, starting with flat stock, has not been done in the past due to the expansion characteristics required. Specifically, hydroforming has not been done with roll bonded sheets specifically configured to create the desired tubes. Because the process is being started with flat stock (rather than a tube), the hydroform fixture must more closely control the way the metal expands.
In order to accomplish this hydroforming, a very unique hydroforming fixture is created which has multi-component die which is specifically configured to accommodate the part being fabricated. Most importantly, the die has various clamps and moveable components which will initially receive and hold the flat stock blank. During the actual hydroforming process thereafter, this fixture will then adjust or move as necessary with the expanding blank. Consequently, over stressing of the aluminum material is avoided during the process.
To provide structural weight bearing capabilities, one embodiment of the finished components utilizes a unique waffle-type pattern which is created via roll bonding. This waffle pattern has a plurality of bond points located throughout its structure. The appropriate placement of a bond inhibitor during the roll bonding process, allows this waffle-type structure to be created. After the roll bonding step is completed, the two sheets of aluminum alloy are separated (at those points where no bond exists), thus creating the three dimensional waffle-type structure as desired.
Due to the three-dimensional structure created, the waffle material allows for greater weight bearing capabilities. More specifically, loads are distributed throughout the structure of the material so that concentrated stress points are avoided.
In order to create these load-bearing structures, two sheets of aluminum alloy material are first chosen of appropriate dimension and thickness. Next, a bond inhibiting material is patterned on one surface of one sheet. The two sheets are then positioned with their major surfaces adjacent one another (and the bond inhibiting pattern therebetween), and are introduced to a roll bonding mill. As well-known, these roll bonding mills have at least two work rolls that are separated by a predetermined distance, and are controlled to provide appropriate pressures to the material sheets introduced therebetween. This creates the desired bond between the material sheets at the desired locations.
Next, an appropriate process is used to separate the sheet material at the unbonded locations. This process may include the use of pressurized air or fluid which is injected between the sheets at the unbonded locations. Further, a forming die may be used to closely control the expansion. This forming process may be very similar to the above discussed process of hydroforming. At this point, the three dimensional waffle-type structure is created which can then be subjected to further operations. For example, additional cutting may be required to achieve a desired configuration. Similarly, bending or other forming operations may be utilized to further form the component into its desired configuration.
Again to allow the efficient use of the roll bonding process in creating this waffled structure, additional steps are necessary to achieve roll bonding of structural grade aluminum. As mentioned above, roll bonding may be accomplished in an enclosed chamber which has a very controlled environment. More specifically, a nitrogen gas, or other appropriate gas may be injected into the chamber and all oxygen removed. This provision would avoid the creation of oxide on the surface of the aluminum sheets. Alternatively, a low temperature, quick preheating step may be used.
It is an object of the present invention to create structural components utilizing the efficient and economical process of roll bonding. Using this process, structural load bearing capabilities are created through the creation of a unique three dimensional structure which evenly distributes and carries the necessary loads.
It is a further object of the present invention to provide load bearing structures, which utilize structural grade aluminum alloys.
It is another object of the present invention to cost effectively create components by using appropriate gauged aluminum materials. This effectively reduces the amount of raw materials used in the processing of structural components, thus also reducing one major cost element.